Buying stuff and hiding

Been having lately some problems with my girlfriend.... we are together for 3 years. And one thing it happen a couple of times was me hiding stuff from her.
my problem is very simple, I like video games, I don't have a massive collection nor I spend hours and hours. But I like to buy games.

and I buy more than actually play. The thing is once I spoke with her about helping me no to buy any games helping me to improve my finances.... but for two times I bought behind her back and she caught me lying in her face about that.....

we have money together, but I always spend my own money. But I have this urge to buy and then I keep hiding from her.... and I don't understand why.

i know it sounds a small problem compare to most people.... but it hurts me that I'm doing this to her.... and I do without any time think about the consequences.

we had another fight a few days ago, I'm trying to find some help, or people that had the same addiction to try to understand why I'm doing this.

been helping talking with strangers.